Cripple Wall Seismic Retrofit

How to Identify a Cripple Wall

If there is a wooden wall on top of a concrete foundation that bears the weight of the floor joists and house above then you have a cripple wall.

The Cripple Wall Problem

There are three common types of seismic vulnerabilities with cripple walls:

1. The sill plate is not bolted to the foundation.
2. The floor joist system lacks a connection to the top plate of the wall unless the home has been built with plywood.
3. There is no lateral stability in the original stacked sheeting (1×8 sheeting) up until the invention of plywood.

The Cripple Wall Seismic Retrofit Solution

1. Connect the sill plate down to the foundation using sill plate bolts with a 3×3 inch bearing plate washer or a Simpson Universal Foundation Plate (UFP). Keep in mind a 3×3 inch bearing plate washer is used to counter uplift forces in the wall and is required by code.
2. Connect the top plate of the cripple wall to the floor joist system using the appropriate hardware.
3. Attach plywood to the wall with continuous nailing to the perimeter of the plywood panel which sometimes requires additional blocking to be installed. The plywood shear panels will take care of the lateral forces delivered by an earthquake which gives the stud system the ability to withstand earthquake forces.